Stroboscope with vibrating cord



Aug. 16, 1927. 1,639,178

A. v. J. GUILLET S'L'ROBOSCOPIEI WITH VIBRATING CORD Filed March 10, 1924 IIIIIIITIIIIII: 1

' f/w 'nror fi KJ 50/7/67 Patented Aug. 16, 1927.

v UNITED STATES AMEDE'E VICTOR JOSEPH GUILLET, or PARIS, FRANCE.

STROBOSCOPE WITH VIBRATIN G CORD.

Application filed March 10, 1924, Serial No. 698,303, and in France March 22, 1923.

This invention relates to stroboscopes.

The requirements of mechanical stroboscopes are that flashes should be produced having a frequency which remains constant 5 at a predetermined value N for. as long a time as is desired and further that there be a possibility of varying this frequency N easlly and continuously. It is further necessary that the value N can be read directly from the stroboscope or obtained from a simple formula.

A stroboscope having a perforated disc does not comply with these conditions, 1n particular, the braking of the motor on the shaft of which the disc is mounted, renders the .stroboscopic operation delicate. With a tuning fork, a fixed flash frequency is indeed obtained but the continuous simultaneous and equal displacement of two identical masses along the arms of such tuning fork cannot be done without diiiiculty. On the other hand the field of frequency which is thus available with the same tuning fork, is relatively limited.

According to the present invention a stroboscope is provided in which the vibratory member is composed of a vibrating cord or string having .a sustained vibratory move- 11161113. A stroboscope formed under these conditions allows of itsbeing operated with full convenience and precision over a considerable field of flash frequency.

It is essential that the vibrating cord shall be mounted in such a way that its vibratory movement is maintained without trouble or disturbance. Various arrangements may be utilized for this object. The annexed drawing shows three of them by way of examples.

Fig. 1 is an elevation of one form of stroboscope. 7

Figs. 2 and 3 are modifications of the vibratory means for such a stroboscope.

Fig. 4 shows a means for adjusting the ten sion of the stroboscope cord or wire.

A steel piano wire a; selected so as to be free from any twist and curvature is firmly held at its ends in two grips a and a (Fig. 1) arranged on a frame I) mounted on a base 6 provided with levelling screws. One of the grips 0. is fixed, the other a 'is movable so as to allow the tension of the cord to be varied as will be hereinafter shown. Opposite the cord at an electro-magnet c is arranged which receives current set up or cut out by the wire itself each time it passes through its position of equilibrium.

The contact must be placed at the extreme end of the cord, that is to say in immediate proximity to its point of attachment. In Fig. 1 the movable contact is shown at d and formed by an envelope of platinum, tungsten, carbon or the like surrounding the cord, and the fixed contact shown at e is carried by an accurate micrometer screw 6 which allows the degree of contact betweend and e to be regulated.

The total work of the forces set up between the cord and the electromagnet is positive and is thusa driving one if the circuit isestablished on the passage through the position of equilibrium when the cord moves away from the elect-romagnet, due to the electric and magnetic dissymmetrical forces which accompany the setting up and breaking of the current.

It is still more efficient to employ the cord a for closing and opening the circuit of a small transformer f (Fig. 2) the secondary current of which excites the electro-magnet 0, the acting element of the'wire being permanently magnetized by an auxiliary circuit a wound on theelectromagnet.

Further the secondary current may in other cases be led into the cord at, which is arranged to be oscillatable perpendicularly to the lines of force of a magnet g surrounding its centre part (Fig.

The movement of the cord tained by one of the means hereinbefore de scribed, flashes are produced by projecting .on to a plate h, which is perforated as with a hole or a slot 71. the image from a luminous source (are or incandescent filament) and fixing in the middle of the cord an extremely light plate 71 also perforated with a hole or slot 2' corresponding with the hole or slot in the plate It. The two apertures 72. and '5 being opposite one another when the cord is at rest, will be in this same position, when the cord will vibrate, each time that the cord will pass through its position of equilibrium, that is to say twice per period. The flash frequency will therefore be 2N if the cord frequency is N.

The modification of this frequency by insensible degrees and over a considerable interval may be obtained by varying the tension of the cord.

v For this purpose the grip 'a of the cord is mounted (Fig. 4) on an internally threaded socket is which may be displaced by means of a screw Z provided with a large head carrybeing thus sus- I ing divisions. It is thus easy to apply to the cord a tension varying continuously and over a wide interval and consequently to bring the frequency N to the value required by the stroboscopic adjustment desired.

The field of frequencies thus explored may lie over several octave intervals and is sufficient for practical purposes. But there is no objection to arranging the cord and the accessory members in such a Way as to utilize successively various lengths of cord or still to mount on the same frame several cords actuated by the same electro magnet, adapted to be arbitrarily substituted one for another.

If it is desired to use a gut string or a string of a non-magnetic metal, the third method of sustaining the vibration hereinbefore described must be employed, or there must be arranged on the string at the point of interaction a soft iron wire.

Stroboscopic harmony having been efl'ected, the frequency is determined by utilizing the following formulae:

2 2 j'fko X (No No me and X2 (N0 mg jfifmc in Which X is the frequency desired, et -n n 'n and n n the displacements of the divisions of the divided head Z when passing from the frequency N to the frequency N and from the frequency X to the frequency N or the frequency N,.

The constant of the stroboscope may be determined either by the direct registration of N and N or still by placing the cord and the tWO diapason types given, in stroboscopic equilibrium. The ascertaining of the positions, a, and n, of the index must be further effected in both cases.

If the variations of the tension of the cord are such that the cord undergoes, in the course of the operations, an appreciable permanent elongation, it is no longer possible to make use of the formulae hereinbefore indicated. v

It Will then be necessary to connect the cord or string firmly with the support by means of a dynamometer or a balance levC' indicating the value of the tension for all given positions of the stretcher. The frequency N is then calculated by applying the known formula giving the fundamental frequency of a stretched cord. The frequency may also be modified by insensible degrees by continuous variations of the length of the cord by means of double bridge sliding along the latter. When it is a question of estimating a frequency producing a regular note like the hem of an axle, the stroboscope forming a cord siren allows of the tuning by beats.

\Vhat I claim is l. A stroboscope, comprising a frame, a vibrating cord, n-ieans for securing said cord at its ends to said frame, means, controlled by the vibrating cord, for producing strobescopic flashes, e-lectro-magnetic means for sustaining the vibration of said cord and means, controlled by the vibrating cord, for supplying current to said electro-magnetic means.

:2. A stroboscopc, comprising a frame, a vibrating cord, means for securing said cord at its ends to said frame, means, controlled by the vibrating cord, for producing stroboscopic flashes, electro-magnetic means adapted to sustain the vibration of said cord, and contact means controlled by the cord.

3. A stroboscope, comprising a. frame, a vibrating cord, means for securing said cord at its ends to said frame, means, controlled by the vibrating cord, for producing stroboscopic flashes, electro-magnetic means for sustaining the vibration of said cord, together with contact members arranged at a point closely adjacent to one of the points of attachment of the cord, for the purpose described.

4. A stroboscopc, comprising a frame, a vibrating cord, means for securing said cord at its ends to said frame, means, controlled by the vibrating cord, for producing strobescopic flashes, electro-magnetic means for sustaining the Vibration of said cord, and means, controlled by the vibrating cord, for supplying current to said electro-magnetic means, together with means for regulating at will, by continuous degrees and within a Wide range, the vibratory frequency of said cord.

5. A stroboscope, comprising a frame, a vibrating cord, means for securing said cord at its ends to said frame, means, controlled by the vibrating cord, for producing stroboscopic flashes, electro-magnetie means for sustaining the vibration of said cord, and means, controlled by the vibrating cord, for supplying current to said electro-magnetic means, together with means for regulating the vibratory frequency of said cord by adjusting the tension thereof.

6. A stroboscope, comprising, a frame, a vibrating cord, means for securing said cord at its ends to said frame, means, controlled by the vibrating cord, for producing stroboscopic flashes, electro-magnetic means for sustaining the vibration of said cord, and means, controlled by the vibrating cord, for supplying current to said electro-magnetic means, a screw stretcher device at one of the ends of the cord for adjusting the tension of the cord.

7. A stroboscope, comprising, a frame, a vibrating cord, means for securing said cord at its ends to said frame, means, controlled by the vibrating cord, for producing stroboscopic flashes, electro-magnetic means for sustaining the vibration of said cord, and means, controlled by the vibrating cord, for supplying current to said electromagnetic means, a screw stretcher device at onetof the ends of the cord for adjustin the 10 tension of the cord, an operating hea on the stretcher device, and graduations on the head.

In testimony whereof I 'have signed my name to this specification.

AMEDEE v. J; GUILLET; 

